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Solar energy could be the world's largest source of power by 2050, providing more than a quarter of the Earth's energy, according to the International Energy Agency (IEA).

A report from the Paris-based agency forecasts that photovoltaic (PV) plants could generate up to 16 percent of the Earth's electricity, while another report says solar thermal electricity (STE), which concentrates sunlight with mirrors to produce steam energy, could provide 11 percent.

The total would push solar energy beyond all other sources of electricity, including fossil fuels, hydropower and nuclear energy. It seems possible because of the "rapid cost decrease" of solar energy hardware, according to a statement by the IEA's executive director, Maria van der Hoeven.

The IEA's conclusions are in line with other forecasts that say renewable energy, particularly solar energy, is set to transform power generation around the world. Bloomberg New Energy Finance expects solar power will increase its share of the energy market by 2030, as the use of panels grows from only 0.3 percent penetration now to fully 6 percent in 15 years.

And the Swiss financial services company USB reported last month that solar power plants and storage devices will become popular enough to change the paradigm of electricity generation.

The IEA, which advises 29 national governments on energy policy, said PV installations have grown much more than agency had expected when it issued its first solar energy outlook in 2010. At that time it saw PVs providing no more than 11 percent of global electrical power by mid-century.

The difference is attributable to the drop in cost and the fact that utilities have responded quickly to that drop, the IEA said. Its latest report notes that more solar capacity has been added since 2010 than was added in the previous 40 years.

As a result, the IEA expects solar facilities to generate about 4,600 gigawatts of PV capacity by 2050, compared with about 150 gigawatts today. But the report stresses that such progress would require a doubling of annual investments into solar energy, to an average of $225 billion per year.

As for solar thermal electricity, the IEA estimates that it generates about 4 gigawatts today, with growth to about 1,000 gigawatts by 2050.

The best news from the IEA is that the use of solar energy will snowball with further price drops and, consequently, greater investment. For example, the agency forecasts an average price drop for PV-generated electricity of 25 percent by 2020, 45 percent by 2030 and 65 percent by 2050.